This application claims the priority of Korean Patent Application Nos. 2003-97246, filed on Dec. 26, 2003 and 2004-89721, filed on Nov. 5, 2004, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to an ultra-wideband (UWB) radio device, and more particularly, to a pulse signal generator for UWB radio transception and a radio transceiver having the same.
2. Description of the Related Art
According to increasing necessity of radio transmission performance and unique location awareness capability of ultra high speed multimedia data of hundreds Mbps through 1 Gbps classes, UWB radio technology is significantly considered in radio communication, imaging, and sensor fields. Basic structures of methods of carrier-free pulse radio devices using the UWB radio technology are already disclosed. Recently, according to permission of commercialization of the radio communication field, various methods of using the UWB radio technology for wireless personal area networks (WPANs) has been suggested.
The UWB radio technology can be largely classified into technology using a single band and technology using a multi-band. In the technology using the single band, there exist a carrier-free pulse-based method and a direct sequence code division multiple access (DS-CDMA) method using a constant carrier. In the technology using the multi-band, there exist a frequency hopping orthogonal frequency division multiplexing (FH-OFDM) method and a multi-band pulse method.
FIG. 1 is a block diagram of a conventional UWB transceiver to which the various radio technologies can be applied.
Referring to FIG. 1, the conventional UWB transceiver includes a radio controller-media access controller (RC-MAC) 110, which is connected to a host or peripherals, an encoder/modulator 120 and a UWB pulse signal generator 130, of which a transmitter is composed, a switch/duplexer 140, an antenna 150, a receiver front-end/correlator 160 and a decoder/demodulator/synchronizer 170, of which a receiver is composed, and a clock/timing generator 180.
FIG. 2 is a block diagram of a conventional UWB transceiver adopting the DS-CDMA method among conventional UWB transceivers.
Referring to FIG. 2, a transmission line, which receives scrambled baseband bitstream data and generates an RF output, a forward error correction (FEC) encoder 202, a preamble prepender 204, a symbol mapper 206, a code set modulator 208, a radio resource controller (RRC)/low-pass filter (LPF) 210, and a multiplier 212. A reception line, which receives an RF input and generates demodulated bitstream data, includes a receiver front-end/correlator 216, a demodulator 218, a synchronizer/channel estimator 220, a decision feedback equalizer (DFE) 222, a deinterleaver 224, and an FEC decoder 226. The conventional UWB transceiver includes a clock/timing generator 214, which provides clock signals and timing signals to the transmission line and the reception line, besides the transmission line and the reception line.
FIG. 3 is a waveform diagram illustrating a UWB impulse signal generated by the UWB transceiver of FIG. 2. FIG. 4 is a power spectrum illustrating the UWB impulse signal of FIG. 3.
Referring to FIGS. 3 and 4, the baseband bitstream data passed through the FEC encoder 202 and the preamble prepender 204 is converted to a spectrum-spread chip signal 301 by passing through the symbol mapper 206 and the code set modulator 208, the chip signal 301 is output as a pulse wavelet type output signal 302 by a pulse generator including the RRC/LPF 210 and the multiplier 212.
In the UWB transceiver, a bandwidth and an out-of-band spurious level are determined according to a pulse wavelet type of the output signal 302. When UWB modules using the conventional DS-CDMA method, whose pulse widths are very narrow, are close within several cm, a performance degradation effect due to interference can occur. The DS-CDMA method requires an equalizer (222 of FIG. 2), which can compensate for time delay spread due to multi-path fading and inter-symbol interference due to the time delay spread. However, it is difficult to realize an equalizer when a data transmission rate is high over hundreds Mbps. Due to this problem, in mobile communication for high speed multimedia communication, the OFDM method or a multi-carrier (MC)-CDMA method in which the OFDM method and the CDMA method is combined method is adopted rather than the DS-CDMA. In particular, the OFDM method or the MC-CDMA method shows excellent performance in a frequency selective fading environment.
A structure of a waveform adaptive ultra-wideband transmitter is disclosed in U.S. Pat. No. 6,026,125. Since the waveform adaptive ultra-wideband transmitter includes an oscillator generating a constant carrier signal and an envelope generator called a low-level impulse generator, the structure of the waveform adaptive ultra-wideband transmitter is very similar to a structure of a transmitter according to the multi-band pulse method. Therefore, in the structure described above, a constant carrier is used, a bandwidth of a transmission wave can be optionally controlled according to filter characteristics of a waveform adapter, and frequency hopping is possible by changing a frequency of the oscillator generating the carrier.
However, a variable range of an output frequency of a general oscillator is not wide such as can accommodate all the frequency range required by a high speed WPAN standard, e.g., 3.1-10.6 GHz, and phase noise increases in proportion to an increase of an oscillator frequency range. A phase modulation method having the highest spectrum efficiency must be used for ultra high speed transmission, and a center frequency of a UWB signal must be exactly designated for signal restoration. To use the phase modulation method and exactly designate the center frequency, a phase lock loop (PLL) must be used. However, the PLL requires a certain time called a lock time until a frequency is changed and stable, and since the lock time is commonly taken over several micro seconds, it is difficult to obtain very fast (within several nano seconds) frequency hopping characteristics required in the multi-band pulse method or the FH-OFDM method with the PLL. Furthermore, the PLL can generate only continuous wave signals not various type pulses. As the results, a UWB DS-CDMA method and the FH-OFDM method cannot be accommodated with one transceiver.